Continuous crimping of yarns

ABSTRACT

A process and apparatus for continuous crimping of thermoplastic heat-settable yarns by the pretwisting of separate yarns into a twisted strand which is then continuously pulled apart at one end while using the rotational movement thus imparted to the strand to feed the individual yarns into the other end of the strand under tension, the strand passing through a heat-setting zone to durably crimp the individual yarns before they reach the separation point where they are pulled apart, the invention being essentially characterized by the step or means of frictionally rotatably driving the strand in the vicinity of the point where the yarns are separated at a drive velocity greater than the peripheral rotational velocity of the strand itself. The process and apparatus are especially useful for very high speed continuous crimping in a twist-detwist manner with uniform results.

United States Patent [191 Schippers m1 3 3,812,664 May 28, 1974CONTINUOUS CRIMPTNG OF YARNS [75] Inventor: Heinz Schippers, Remscheid,

Germany [73] Assignee: Barmag Barmer Maschinent'abrikAktiengosellschaft, Wuppertal, Germany 22 Filed: July 26, 1972 211 Appl.No.: 275,174

52 u.s.c|. 57/34 HS,S 7/77.4,57/157TS [51] Int. Cl D02g 1/02 [58] Fieldof Search... 57/34 R, 34 HS, 77.3-77.4 S;

57/l'57 R, 157 MS, 157 TS [56] References Cited UNITED STATES PATENTS3,413,796 12/1968 Comer et al. 57/34 HS X 3,423,924 H1969 Comer et al.57/34 HS X 3,643,4l2 2/1972 Maeda et al 57/34 HS Primqry Examiner-DonaldE. Watkins Attorney, Agent. or Firm-Johnston, Keil, Thompson 7 &Shurtleff 5 7 1 ABSTRACT A process and apparatus for continuous crimpingof thermoplastic heat-settable yarns by the pretwisting of separateyarns into a twisted strand which is then continuously pulled apart atone end while using the rotational movement thus imparted to the strandto feed 'the individual yarns into the other end of the strand undertension, the strand passing through a heatsetting zone to durably crimpthe individual yarns before they reach the separation point where theyare pulled apart, the invention being essentially characterized by thestep or means of frictionally rotatably driving the strand in thevicinity of the point where the yarns are separated at a drive velocitygreater than the peripheral rotational velocity of the strand itself.The process and apparatus are especially useful for very high speedcontinuous crimping in a twist-detwist manner with uniform results.

I 9 Claims, 14 Drawing Figures fATENTEDMAY 28 1914 sum 1 0r 2 FIG. 4b

FIG. 4a

mmrmm m4 3312.664 SHEET 2 OF 2 WNWQ 3:: In 3 1 CONTINUOUS CRIMPING OFYARNS referred to as the twist-detwist method, two or more separatethreads or yarns are twisted or coiled with one another into a twistedstrand, subjected to heatfixing or heat-setting and then separated againinto individual crimped threads, each of which can be collected or woundup by itself.

For the initiation of such a separation twist procedure, the ends of twoor more threads situated on separate feed bobbins or pirns are broughttogether and pretwisted with one another to form a twisted lengthorstrand over a predetermined length. In such twisting, each individualthread or yarn can also be turned about its own axis so that thereexists a true twist of two or more yarnsv lf the threads or yarns arewound about one another without the individual yarn being turned on itsown axis, one speaks ofa cooling of the yarns.

ln this application, the term twisting" isused generically to includeand have the same meaning as the term coiling. Also, the term yarn isused herein in its generic sense so as to apply to threads, tows andother filamentary forms of all typical thermopastic fibrous materials,especially the synthetic linear fiber-forming polymers such as thepolyamides (nylon 6, nylon 66), polyesters (polyethylene.terephthalate), polyolefins (polypropylene) or the like.

Through this pretwisting of two or more individual yarns, there isprovided the so-called twisted strand which has a length and a number ofturns'per unit length as predetermined at the beginning of theseparation twist process. The yarn ends which are separated and takenfrom this twisted strand may then be separately fed each to a winding orcollection bobbin. The windings of the heat-fixed or heat-set yarns canalso be formed on a single collection sleeve or tube. It is also anexpedient and known practice to conduct the yarns after their separationfrom the twisted strand by means of yarn guides and/or draw-off rollers,godets, nip rolls or similar arrangements. After setting into operationthe draw-off roller or winding bobbins, the yarns are drawn off fromtheir feed bobbins into the twisted strand so as to be twisted with oneanother, subjected to a heat-fixing or heat-setting i.e., a heattreatment of the twisted strand and a subsequent cooling thereof, afterwhich the individual yarn ends are again drawn apart under a certaintensional force and wound up or collected separately. In thisseparation-twist process, there is formed a so-called natural orfloating separating point, i.e., the point at which the individual yarnsin the twisted strand separate under the lateral or tensional forcesacting to pull them apart.

Through the heat-setting of the twisted strand, each individual yarnundergoes a crimp formation. Crimping and qualityof the crimped threadsor yarns produced in a typical separation twist process as well as theproduction speed are limited by the fact that the separation of two ormore yarns from the twisted strand presents a number of difficulties. l

The separation of the yarns and the tension thereby exerted on the yarnsexerts a torsional moment on the twisted strand. Excessively hightension on the yarns leads to a twisted strand which is too stronglytwisted and forms knots or nodules. This can then lead to a breakage ofone or more filaments of the yarns. Where the yarn tension is notconstant, especially at the feed side, the so called floating separationpoint moves upward or downward in a vertical direction, i.e.,substantially in the vertical direction usually occupied by the twistedstrand. The length of the twisted strand thus changes so as to vary theturns per unit length in the strand and thereby the crimping number. Itis also important that the yarns twisted together in the strand aredrawn apart with equal or at least uniform tension. In the mostexceptional case, the yarn drawn off with the highest tension remainsuncrimped because it has remained untwisted, while the other yarn oryarns have been laid or coiled around it in windings. Unequal orvariable yarn tensions lead to the result that the floating separationpoint migrates in the direction of the yarn drawn off with the greaterforce.

Many proposals'to solve such problems have been made to achieve someimprovement. According to German Pat. Application No. 1,435,477, it isproposed that the draw-off tensionof each yarn after the separationpoint be regulated with the aid of a regulating element which isoperated in dependency upon the lateral deviation of the floatingseparating point. According to US. Pats. No. 3,091,908 and No.3,327,462, thetensions of the yarns running apart in differentdirections are controlled by means which reduce draw-off speed inresponse to yarn tension. It is further indicated that excessively greatdisplacement of the separating point in a verticaldirection can bepreventedby thread or yarn guide elements arranged laterally after theseparating point (for example, note US. Pat. No. 3,327,462, column 4,lines 2 to 8) Simultaneously, however, these guide elements representthe extreme limit to which the separating point can stray laterally.

None of these prior measures eliminate the cause for the fluctuations ofthe thread tension. Accordingly,

such methods and apparatus can only provide a relative evening orsmoothing out of the yarn tensions through regulating or stabilizingmeans, especially since the control of the yarn tensions is alwayssubject to inertia and the yarn tensions change quite rapidly and undersome circumstances in sudden and pronounced leaps. The remainingdeviation of the separating point, even when relatively slight, stillleads to an uneven crimping effect. Furthermore, the control of the yarntensions, especially if it takes place through a necessary reduction ofthe draw-off speed, results in a simultaneous reduction of theproduction speed.

One object of the present invention is to overcome these drawbacks andserious disadvantages by providing a separation twist process andapparatus which, at the highest production speed, produces heat-settextured yarns of constant crimping. It is also an object to eliminatethe danger of yarn or filament breakage as a consequence of thetorsional moment being provided at the separating point and the yarntensions required for this purpose.

Another object of the invention is to provide a separation twistapparatus whereby the floating separation point of the yarns beingpulled apart is much less dependent upon variations in the feed and drawtensions of the individual yarn ends, the separation point still beingstabilized in its position through improved twist or torque regulatingmeans. Other objects and advantages of the invention will become moreapparent upon consideration of the following detailed disclosure.

It has now been found, in accordance withthe invention, that asubstantial improvement can be achieved in such a process for thecontinuous crimping of a thermoplastic heat-settable yarn 'whereinseparate yarns are pretwisted together over a predetermined length toform a twisted strand which is heated and then cooled under tension in aheat-setting zone and wherein said yarns are continuously separated bybeing pulled apart at one end of said twisted strand while continuouslyfeeding the separate yarns together into said twisted strand at theother end thereof, thereby imparting a rotational movement to saidstrand, the improvement residing in the step which comprisesfrictionally rotatably driving the twisted strand in the vicinity of thepoint where the yarns are separated at a drive velocity which is greaterthan the peripheral velocity of the rotational movement of the stranditself.

In order to keep the required surface or contact pressure between thefriction drive and twisted strand as low as possible, it is furtherproposed to carry out the separation twist process of the invention suchthat the frictional drive velocity on the twistedstrand decreases towardthe separating point of the two or more yarns.

An especially useful separation twist appatatus for carrying out thecontinuous heat-set crimping of a thermoplastic yarn is a combinationwhich comprises, in addition to conventional heating and cooling meansforming a heat-setting zone, yarn feed and withdrawal means tocontinuously transport a rotating twisted strand of individual yarnsunder tension through the heat-setting zone, this withdrawal meansacting to pull apart and separate the individual yarns from each otherat a point of separation of the twisted strand following theheat-setting zone, and a frictional torque assembly positioned along thetwisted strand in the vicinity of the point of separation and acting tofrictionally drive the twisted strand on itsouter periphery.

To provide a gradually reduced frictional drive velocity over a lengthof the twisted strand in its direction of longitudinal travel, thefrictional torque assembly can be constructed with a conicalconfiguration, e.g., either as conically formed drive rolls with theconical apexdirected toward the separating point of the yarns or else asa plurality of friction wheels which are arranged successively along thetwisted strand and which become smaller in diameter toward theseparating point of the individual crimped yarns.

In the process and apparatus of the invention, the rotatable frictiondrive of the torque assembly can be driven at such a speed and at such aContact or bearing pressure on the twisted strand that the torsionalmoment introduced in this manner into the strand is smaller than thetorsional moment of the twisted strand itself. In this casetheindividual yarns are finally separated only by exertion of a positiveseparating pull or draw tension, so that a separating point is formedfollowing the frictional torque assembly. In order to prevent anyexcessive lateral or vertical excursion of the separating point underthese conditions, it is preferable separating point of the yarns liesbetween the output of the frictional torque assembly and the yarn guidemeans. 1

In a preferred embodiment, it is further proposed according to theinvention that the frictional torque assembly be arranged in such amanner that the separating point of the yarns lies in the torqueassembly itself, i.e., this assembly preferably including at least twofrictional drive members arranged at the point of separation of theindividual yarns to simultaneously act as yarn guide means in directingeach of the separated yarns in a different path outwardly from the pointof separation. In this case, the torsional moment exerted by thefrictional drive means of the torque assembly on the twisted strand canbe so great that the separation of the yarns occurs without exertion ofan especially high pull force or draw tension on the separated yarns. Itis also possible, however, for a smaller torsional moment to be providedby the frictional torque assembly, so that the threads must be separatedunder additional pull or draw tension. In every case in this preferredarrangement, an excursion of the separating point is virtuallycompletely prevented and the position of this floating point ofseparation ishighly stabilized.

For a-further detailed description of the invention, reference is madeto the particular embodiments described by way of example hereinafter inconjunction with the accompanying drawingswherein:

FIG. 1 is a schematic representation of the process and conventionalapparatus for continuous crimping by separation twisting;

FIGS. 2a and 2b illustrate twisted and coiled yarns respectively;

FIG. 3a is an enlarged view of yarn segments at the separation point astaken from FIG. 1

FIG. 3b shows the same yarn segments as FIG. 3a but with reduced tensionor pull force on theyarns being separated; I

FIG. 30 shows the same yarn segments as FIG. 30 but with increasingtension or pull force on the yarns being separated;

FIGS. 4a and 4b illustrate portions taken from FIG. 1 with unequal yarntension in the yarns being separated;

FIGS. 5 through 9 illustrate a number of different embodiments of thecombination for separating twisting apparatus according to theinvention; and

FIG. 10 illustrates a preferred overlapping arrangement of threefriction wheels as torque drive means in a false-twist assembly of theinvention.

In FIG. 1, from the run-off or feed bobbins 1 and I there are drawn twoyarns Y and Y which are conducted over a delivery system such as thefeed roller pairs 2 and 2 and then drawn through converging paths into atwisted strand 3 which has been initially produced with a predeterminedlength and degree of twist of the yarns according to the required crimp.In

= a heat-setting zone 6, by means of a heating device 7 and any suitablecooling device 8, the twist of the yarns is fixed. At the separatingpoint 5, the textured yarns 4 and 4' are pulled apart in diverging pathsby means of the draw-off rollers 9 and 9' and wound onto the takeupreels or bobbins l0 and 10. This conventional process can also becarried out with more than two yarns although, to be sure, the crimpingis less. The delivery or feed rolls 2 and 2' can also be omitted orpreferably replaced or supplemented by thread or yarn brakes.

Such braking means on the yarn feed make it possible for the yarn to runinto the twisted strand 3 at the necessary high yarn tension required toexert on the strand the rotation or torsional moment for twisting. Also,as is known, tension on the twisted strand 3 is desirable in maintainingthe necessary contact with the heating means 7 which can best be in theform of a conventional heating plate or the like, e.g., one which isslightly curved and pressed slightly outwardly against the travellingtwisted strand.

It is of particular advantage that the feed and withdrawal meansaccording to the invention can be of any usual construction and need notbe specially designed for stabilizing the yarn separation point, i.e.,with the rather complicated mechanisms now required for this process. Atthe same time, the present invention does not exclude such additionalstabilizing means which may offer some additonal benefit in adjusting ormaintaining the separation point.

The present invention is particularly concerned with the use of arotating or torque drive means applied to the twisted strand at theseparating point 5, as described more fully below, so that the zoneimmediately following the cooling means 8 is significant, especiallythat zone in the vicinity of the separating point represented by thesegments enclosed by A, B and C.

The yarns can be twisted or coiled with one another in the twistedstrand 3. As represented in FIG. 2a, the individual yarns Y and Y duringtheir twisting are each turned simultaneously about the other and alsoabout their own axis. Thus, a displacement of the real or imaginaryfilaments al, a2 and bl, b2 of the yarn takes place relative to the yarnaxis. In the so-called coiling," as represented in FIG. 2b, in contrast,the individual imaginary or real filaments of the yarn retain theirposition parallel to the yarn axis, i.e., the yarns are not turned ortwisted about their own axis.

The heating device 7 can be operated according to any desired system,e.g., by convection, radiation or heat conduction, and can be of anyconventional construction. Special cooling means 8 can be arranged forthe cooling zone such as, for example, a blower or fan using cooled airor even air at room temperature with a sufficiently long cooling zone.The yarn path of the strand 3 in the cooling zone 8 can even be so longthat special cooling apparatus is unnecessary, the cooling beingaccomplished simply by running the strand 3 is a normal atmosphere,i.e., at prevailing room conditions.

The position of the separating point 5 depends on the torsional momentunder which the twisted strand 3 has been placed by the pretwist and bythe tension with which the yarns 4 and 4' are drawn off. The angle underwhich the threads are drawn off is equal to the pitch angle 11 at whichthe threads are twisted with one another in the zone of the separatingpoint 5 as illustrated for example in FIG. 3a. In FIG. 3b there isrepresented the manner in which the separating point strays upwardly inthe case of a reduced torsional moment with increasing pitch angle 11 ofthe twisted strand 3. FIG. illustrates how the separating point straysdownwardly with increasing torsional moment and a decreasing pitch angle11.

FIGS. 4a and 4b indicate the lateral excursion of the separating point 5in the case of unequal tension in the two yarns 4 and 4'. In the extremecase, the yarns in the twisted strand 3 are not twisted together butinstead the yarn 4 in FIG. 4a or yarn 4' in FIG, 4b is coiled in ahelical winding or spirals around the yarn under such a strong tensionthat it remains practically linear, e.g., as suggested by 4' in FIG. 4b.This technique is sometimes adopted where one yarn is replaced by acontinuous loop thread or wire but still remains difficult to controlexcept by carefully regulating the unbalanced tensions.

Both the vertical and also the lateral excursion of the separatingpoint, which proceed very rapidly and can be brought about through anunevenness inone or both yarns, e.g., by nodules or the like in thetwisted strand, lead to non-uniform crimping and under somecircumstances to yarn or filament breakage.

In the embodiment of the present invention which is represented in FIG.5, the twisted strand 3 is driven on its periphery by means of thefrictional torque assembly 12 which consists of two friction wheels 13and 13'. It will be understood that these wheels or any other torquedrive means of the invention always rotate and, namely, in the samedirection according to the rotation in which the twisted strand turnsnaturally as the yarns are withdrawn at 4 and 4. Otherwise, theconstruction of the apparatus and the sequence of process stepscorresponds to that shown in FIG. 1. In other words, the torque drivemeans such as wheels 13 and 13 should be positively driven preferably atthe same rate, by any suitable motor or drive linkage such as thevariable speed motors M, so that the drive velocity proceeds in the samedirection at tangential contact points with the strand 3 but with agreater velocity than that of the peripheral or circumferential speed of'the strand itself.

The frictional torque assembly can be of any convenient type ofconstruction. It can consist, for example, of one or several coaxiallyarranged wheels of the same diameter. It can also be constructed as arotatably mounted sleeve which drives the twisted strand on the innerperiphery of the sleeve. There can also be provided three frictionaldrive wheels or three groups of drive wheels which rotate on three axlesarranged in a triangle, the wheels overlapping in such a way that thethread can be conducted through between them in axial direction andsubstantially in a straight line while being in frictional contact withthe circumference of each wheel (cf. FIG. 10).

This complementary rotation or torque being applied to the twistedstrand is used to resolve or even substantially cancel the normal.rotation or torsional moment produced by the draw means 9 and 9'. Theamount of torque applied by the assembly 12 is thereby positively usedto control the torsional moment placed on the strand 3, the amount oftension in the yarns 4 and 4' and also the position of the separatingpoint 5.

In the example shown in FIG. 5, the rotation of the twisted strand 3 isin part resolved by the frictional drive wheels 13 and 13. The pitchangle 11 of the twisted strand before the frictional torque assembly 12is smaller than the pitch angle 11' following the torque assembly.

In FIGS. 6, 7 and 8, the twisted strand 3 is driven on its peripherywith a drive velocity which decreases toward the separating point 5. InFIG. 6, this is accomplished by the conical frictional drive rolls l4and 14'. In FIG. 7, four coaxially arranged friction wheels 15 becomesmaller in diameter toward the separating point 5 to provide a similarconical configuration in stages, the yarn guides 17 cooperating to laythe twisted strand 3 against the circumference of each friction wheel15. Still another embodiment is shown in FIG. 8 and includes a rotatingconical sleeve 16, which drives the strand 3 at the input and outputedges of the sleeve inner periphery which can be suitably rounded orbeaded as shown. This sleeve can be gear or belt driven when mountedrotatably as indicated. Otherwise, the construction of the separationtwist apparatus and the course of the process according to FIGS. 6, 7and 8 corresponds to that of FIGS. 1 and 5. 7

in FIGS. 6 and 8 there is additionally provided the yarn guide 18. Thisfixed guide 18, is arranged in such a way that the separating point liesbetween the output of the torque or false twist assembly 'l2 and theguide l8. The spacing between the two is relatively small and the yarnguide 18 is narrow in diameter (having been greatly exaggerated in thedrawing). This assures that the separating point of the yarns can strayonly slightly in the case of uneven yarn tension in one or both yarns. 1

In FIG. 9, which otherwise corresponds to FIG. 5, the twisted strand 3is driven at such a high velocity or with such slight slippage, that thetwisting (Verdrehung) is already cancelled in the frictional torqueassembly 12.

There, the separated threads 4 and 4' are drawn off in such a directionthat the rounded edges 19 and 19 of the friction wheels 13 and 13' serveas the yarn guides. An excursion or straying of the separating point 5is virtually impossible in this embodiment and the device is especiallydistinguished in that it is surprisingly selfregulating.

For the apparatus constructed and operated accord- 7 ing to FIG. 9, itis particularly advantageous to provide a frictional torque assembly 12constructed as shown in FIG. 10.. The three friction wheels 20, 20' and20" have their axes arranged in atriangle in such a way that the wheelsoverlap and the twisted strand 3 can be threadedthrough and betweenthese wheels very nearly in a straight line and in contact with theouter circumference of each of the wheels.

A special advantage of the invention resides in the fact that it becomespossible to eliminate the causes of thread tension fluctuations and theconsequential displacement of the separating point, fluctuations in thecrimpingand filament or yarn breakages, while hitherto it was onlypossible to keep the efi'ects of yarn tension fluctuations withinlimits, e.g., by more or less stabilizing the yarn separation point. Theinvention permits a much stronger twisting of the yarns in the twistedstrand and thereby a stronger crimping with increased production speedand output of a very uniformly textured yarn.

The invention is hereby claimed as follows:

I. In a separation twist process for the continuous crimping of athermoplastic heat-settable yarn wherein separate yarns are pretwistedtogether over a predeter mined length to form a true twisted strandwhich is heated and then cooled under tension in a heat-setting zone andwherein said yarns are continuously separated by being pulled aprat atone end of said twisted strand while continuously feeding the separateyarns together into said twisted strand at the other end thereof,thereby imparting a rotational movement to said strand, the improvementwhich comprises: frictionally rotatably driving the twisted strand inthe vicinity of the point where the yarns are separated at a drivevelocity which is greater than the peripheral velocity of the retational movement of the strand itself and with said drive velocity onsaid twisted strand being decreased toward the point where the yarns areseparated.

2. A process as claimed in claim I wherein the yarns being separated arepulled outwardly over a fixed guide surface and the point of separationis maintained between said guide surface and the preceeding frictionaldrive contact on the twisted yarn.

3. A process as claimed in claim I wherein the point where the yarns areseparated is maintained at about the last point of frictional drivecontact on the twisted yarn.

4. A separation-twist apparatus for the continuous heat-set crimping ofa thermoplastic yarn which comprises:

yarn feed and withdrawal means to continuously transport a rotatingtwisted strand of individual yarns under tension through a heat-settingzone, said withdrawal means acting to pull apart and separate theindividual yarns from each other at a point of separation of the twistedstrand following said heat-setting zone; and

a frictional torque assembly positioned along the twisted strand in thevicinity of said point of separation, said assembly including drivemeans arranged to frictionally rotate said twisted strand at tangentialcontact points along its outer periphery with successively reduced drivevelocities toward the point where the yarns are separated.

5. Apparatus as claimed in claim 4 wherein said frictional torqueassembly has a conical configuration with reference to its surfaceswhich are in driving contact with the twisted strand, the conical apexbeing directed toward said point of separation of the individual yarns.

6. Apparatus as claimed in claim 4 wherein said torque assembly includesa plurality of frictional drive wheels arranged successively along thetwisted strand with their diameters becoming smaller toward said pointof separation of the individual yarns.

7. Apparatus as claimed in claim 4 including yarntransport a rotatingtwisted strand of individual yarns under tension through a heat-settingzone, said withdrawal means acting to pull apart and separate theindividual yarns from each other at a point of separation of the twistedstrand following said heat-setting zone; and

a frictional torque assembly positioned along the twisted strand in thevicinity of said point of separation and acting to frictionally drivesaid twisted strand on its outer periphery, said frictional torqueassembly including a set of at least two frictional drive membersarranged at said point of separation of the individual yarns tosimultaneously rotate the yarn and act as yarn guide means in directingeach of the separated yarns in a different path outwardly from the pointof separation.

9. Apparatus as claimed in claim 8 wherein said frictional torqueassembly includes three frictional drive wheels arranged at said pointof separation in overlapping relationship for tangential contact withthe periphery of said twisted strand at about equal intervals around thestrand circumference.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 1 661;Dated May 98 107A Invent r( Heinz Schippers It is certified that errorappears in the above-identified patent and that said Letters Patent arehereby corrected as shown below:

First page, left-hand column, ninth line, insert 30 Foreign ApplicationPriority Data July 27, 1971 Germany P 21 37 451.6

Column 5, line &7, "is should read in Column 7, line 60, "aprat" shouldread apart Signed. and Scaled this A I test:

RUTH C. MASON C. MARSHALL DANN Arresting Officer Commissioner ofla tentsand Trademarks

1. In a separation twist process for the continuous crimping of athermoplastic heat-settable yarn wherein separate yarns are pretwistedtogether over a predetermined length to form a true twisted strand whichis heated and then cooled under tension in a heat-setting zone andwherein said yarns are continuously separated by being pulled aprat atone end of said twisted strand while continuously feeding the separateyarns together into said twisted strand at the other end thereof,thereby imparting a rotational movement to said strand, the improvementwhich comprises: frictionally rotatably driving the twisted strand inthe vicinity of the point where the yarns are separated at a drivevelocity which is greater than the peripheral velocity of the rotationalmovement of the strand itself and with said drive velocity on saidtwisted strand being decreased toward the point where the yarns areseparated.
 2. A process as claimed in claim 1 wherein the yarns beingseparated are pulled outwardly over a fixed guide surface and the pointof separation is maintained between said guide surface and thepreceeding frictional drive contact on the twisted yarn.
 3. A process asclaimed in claim 1 wherein the point where the yarns are separated ismaintained at about the last point of frictional drive contact on thetwisted yarn.
 4. A separation-twist apparatus for the continuousheat-set crimping of a thermoplastic yarn which comprises: yarn feed andwithdrawal means to continuously transport a rotating twisted strand ofindividual yarns under tension through a heat-setting zone, saidwithdrawal means acting to pull apart and separate the individual yarnsfrom each other at a point of separation of the twisted strand followingsaid heat-setting zone; and a frictional torque assembly positionedalong the twisted strand in the vicinity of said point of separation,said assembly including drive means arranged to frictionally rotate saidtwisted strand at tangential contact points along its outer peripherywith successively reduced drive velocities toward the point where theyarns are separated.
 5. Apparatus as claiied in claim 4 wherein saidfrictional torque assembly has a conical configuration with reference toits surfaces which are in driving contact with the twisted strand, theconical apex being directed toward said point of separation of theindividual yarns.
 6. Apparatus as claimed in claim 4 wherein said torqueassembly includes a plurality of frictional drive wheels arrangedsuccessively along the twisted strand with their diameters becomingsmalleR toward said point of separation of the individual yarns. 7.Apparatus as claimed in claim 4 including yarn guide means immediatelyfollowing the frictional torque assembly and positioned to receive anddirect each of the separated yarns in a different path outwardly fromsaid point of separation.
 8. A separation-twist apparatus for thecontinuous heat-set crimping of a thermoplastic yarn which comprises:yarn feed and withdrawal means to continuously transport a rotatingtwisted strand of individual yarns under tension through a heat-settingzone, said withdrawal means acting to pull apart and separate theindividual yarns from each other at a point of separation of the twistedstrand following said heat-setting zone; and a frictional torqueassembly positioned along the twisted strand in the vicinity of saidpoint of separation and acting to frictionally drive said twisted strandon its outer periphery, said frictional torque assembly including a setof at least two frictional drive members arranged at said point ofseparation of the individual yarns to simultaneously rotate the yarn andact as yarn guide means in directing each of the separated yarns in adifferent path outwardly from the point of separation.
 9. Apparatus asclaimed in claim 8 wherein said frictional torque assembly includesthree frictional drive wheels arranged at said point of separation inoverlapping relationship for tangential contact with the periphery ofsaid twisted strand at about equal intervals around the strandcircumference.